Re: POSIX Message Queue Priority Scheduling

[Jonathan Haws <Jonathan.Haws@sdl.usu.edu>]

> > Can someone explain to me how message queues handle waking multiple
> > threads blocked on a single message queue?
> > 
> > My situation is I have multiple writers blocking on a full message
> > queue, each posting messages with priority equal to the thread
> > priority.  I want to make sure they wake and post in priority
> > order,
> > however my application is behaving as if they are waking in FIFO
> > order
> > (i.e. the order in which they blocked).  Each blocking thread is
> > scheduled with the SCHED_FIFO policy with a different priority with
> > system level scope.
> > 
> > I've searched the Internet high and low for something describing
> > how
> > this should work and all I can find is POSIX man pages describing
> > that
> > multiple blockers wake in priority order **if Priority Scheduling
> > is
> > supported**.  Since the kernel scheduler is a priority scheduler I
> > would think that the threads would wake in priority order and post
> > to
> > the queue, however that doesn't appear to be the case.  I'm sure
> > I'm
> > just missing some subtle detail and was hoping the experts here on
> > this list can help shine some light on what I'm seeing, since its
> > at
> > the kernel level that these threads are made ready to run.
> > 
> > I have a small test application that I can post here if
> > necessary.  If
> > this isn't the right place to ask this, by all means let me know
> > and
> > direct me to the right forum.

Bump...anyone have any thoughts on this?  I haven't been able to find
anything on this.